Re: st: Adding normal density to overlayed histograms

["Michael N. Mitchell" <Michael.Norman.Mitchell@gmail.com>]

Dear Dorothy

  The documentation for -help addplot_option- indicates that the -addplot()- option shows 
that it works like this...

. sts graph, addplot(your_contribution)

the result is that the commands construct

. graph twoway something_complicated || your_contribution

  so your command would translate into

. graph twoway hist x, normal || hist x2, normal

  but, unfortunately, -normal- is not a supported option for -graph twoway-, it is only 
supported for -hist- alone.

  Using the -auto- dataset as an example, here is a long way you can create an overlaid 
histogram of -weight- and -price- with a normal overlay for each...

- snip -
sysuse auto, clear

hist weight, addplot(hist price)

summarize weight
local m1 = r(mean)
local s1 = r(sd)

summarize price
local m2 = r(mean)
local s2 = r(sd)

graph twoway (histogram weight) ///
             (histogram price) ///
             (function normden(x,`m1',`s1'), range(weight)) ///
             (function normden(x,`m2',`s2'), range(price))
- snip -

  I hope that helps,

Best regards,

Michael N. Mitchell
Data Management Using Stata      - http://www.stata.com/bookstore/dmus.html
A Visual Guide to Stata Graphics - http://www.stata.com/bookstore/vgsg.html
Stata tidbit of the week         - http://www.MichaelNormanMitchell.com



On 2010-10-20 9.39 PM, Dorothy Bridges wrote:
> Hi everyone,
>
> I am overlaying two histograms and would like Stata to add a normal
> density curve for each.
>
> hist x, normal addplot(hist x2)
>
> works fine, but
>
> hist x, normal addplot(hist x2, normal)
>
> tells me that normal is not an option.  Any ideas as to why this is happening?
>
> Thanks,
> Dorothy
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